US Weather Whirlygig: From Spring Heat to Arctic Chill

Many Americans are bracing for a significant change in weather as a week of spring-like temperatures, which saw many states 15-20C above average, gives way to a polar airmass. This incoming cold front is expected to bring freezing conditions and snow across the country. The extreme temperature variations are not isolated to North America; São Paulo, Brazil, recently recorded its highest-ever December temperature at 36.2C, with this heat expected to spread to other parts of South America.

Meanwhile, Japan is experiencing severe winter conditions. Heavy snowfall and icy roads led to a fatal highway pileup in Gunma prefecture, resulting in two deaths and numerous injuries. Forecasters predict continued heavy snowfall due to Siberian winds interacting with the Sea of Japan, a phenomenon known as "sea-effect" snow, impacting northern and western regions.

New Zealand's South Island has been hit by intense summer storms, including torrential rain, large hail, and lightning, causing travel disruptions. A powerful "supercell" storm was observed over the Canterbury Plains. Further severe weather, including strong winds and heavy rainfall up to 200mm in western areas, is forecast for the North Island as a low-pressure system moves through.